Tech Briefs

Lithium Alkoxide Electrolyte Additives for Lithium-Ion Cells

These additives help to extend operating temperatures to as low as –40 °C.

Alkoxides of lithium have been found to be useful as electrolyte additives to improve the low-temperature performance of rechargeable lithium-ion electrochemical cells. As explained below, an additive of this type exerts beneficial electrochemical effects both within the bulk of the electrolyte and on the surface of the carbon anode, such that the low-temperature electrical characteristics of the cell are improved.

Posted in: Briefs, TSP, Materials, Battery cell chemistry, Lithium-ion batteries, Battery cell chemistry, Lithium-ion batteries, Electrolytes, Materials properties

Aliphatic Ester Electrolyte Additives for Lithium-Ion Cells

Higher-molecular-weight esters show promise for extending lower temperature limits.

Aliphatic esters have been found to be useful as electrolyte additives for improving the low-temperature performances of rechargeable lithium-ion electrochemical cells. The discovery of the beneficial effects of these additives was made during continuing research directed toward extending the lower limit of operating temperatures of these cells. Other aspects of this research have been described in the immediately preceding article and in prior NASA Tech Briefs articles referenced therein.

Posted in: Briefs, TSP, Materials, Battery cell chemistry, Lithium-ion batteries, Battery cell chemistry, Lithium-ion batteries, Electrolytes, Materials properties

Ethyl Methyl Carbonate as a Cosolvent for Lithium-Ion Cells

A low freezing temperature and low viscosity contribute to low-temperature performance.

Ethyl methyl carbonate (EMC) has been found to be a suitable cosolvent, along with three other carbonate solvents, for incorporation into electrolytes to enhance the low-temperature performance of rechargeable lithium-ion electrochemical cells. EMC is an asymmetric aliphatic carbonate, and, as noted in the first of the two immediately preceding articles, asymmetric carbonates confer certain benefits. In the research described in that article, the asymmetric carbonates were formed in situ, in reactions catalyzed by lithium alkoxide additives. In contrast, the present finding that EMC is a suitable cosolvent was made by following a different approach; namely, formulating the electrolyte solvents to include an asymmetric aliphatic carbonate — EMC — in the first place.

Posted in: Briefs, TSP, Materials, Lithium-ion batteries, Lithium-ion batteries, Chemicals

Rechargeable Li-Ion Cells Containing TiS2 Anodes

Low-temperature performances exceed those of cells containing graphite anodes.

Titanium disulfide has been found to be attractive as an alternative to graphite as the anode material in rechargeable lithium-ion electrochemical cells that are required to operate at temperatures below -20 °C. By using TiS2 as the anode material, LiCoO2 as the cathode material, and a suitable low-temperature electrolyte described below, it is possible to construct cells that exhibit superior low-temperature characteristics, including relatively high charge/discharge capacities, capabilities for charging and discharging at relatively high rates, and excellent retention of capacity after repeated charge/discharge cycling.

Posted in: Briefs, TSP, Materials, Lithium-ion batteries, Lithium-ion batteries

Expendable Composite-Layup Dies From Rapid-Prototype Masters

Small production runs of intricate parts can be accomplished at relatively low cost.

A method that exploits rapid prototyping has been conceived to reduce the time and cost associated with the production of small quantities of composite-material parts that have complex shapes. In this method, mandrels and dies used in forming composite layups are sized and shaped by molding them on rapid-prototype masters and are made of disintegrating mold material (DMM). The method is particularly suitable for manufacturing ventilating air ducts and water ducts for the International Space Station and manifolds and ducts for low-temperature [

Posted in: Briefs, Manufacturing & Prototyping, Rapid prototyping, Composite materials

Punches and Dies for Rounding Corners of Metal Sheets

Corners can be formed to desired radii without sawing, snipping, or filing.

Punch-and-die sets have been designed for use in rounding corners of rectangular metal sheets to specified radii. One of the traditional procedures for rounding a corner on a rectangular metal sheet is to first make a rough cut with a band saw and/or hand metal snips, then to file the roughly cut edge; this procedure is time-consuming and does not result in an accurate radius. The use of a punch-and-die set of the present type takes less time and results in a corner with an accurate radius.

Posted in: Briefs, TSP, Manufacturing & Prototyping, Cutting, Manufacturing equipment and machinery, Stamping, Metals

Model of Pyrolysis of Biomass in a Fluidized-Bed Reactor

Complex dynamics and heat transfer are represented more realistically than in prior models.

A mathematical model has been formulated to describe the pyrolysis of biomass in a bubbling fluidized-bed reactor. The reactor is a vertical cylinder that contains a mixture of biomass particles and sand. Superheated steam enters the reactor through holes in the bottom and flows out freely at the top. The sand is a high heat capacity medium used for heating the biomass. The biomass particles, initially at room temperature, are introduced into the already hot reactor and become heated primarily through contact with the sand. Upon reaching a threshold temperature, the biomass particles undergo chemical reactions, the gaseous products of which are carried away by the flow of steam. The "bubbles" are regions of the fluidized bed that are mostly devoid of particles; these regions occur as a result of the interaction of the turbulent gaseous flow with the particles.

Posted in: Briefs, TSP, Physical Sciences, Thermodynamics, Thermodynamics, Biomaterials, Chemicals, Gases, Test equipment and instrumentation

System for Delivering Gas Samples to Multiple Instruments

A system that samples gases at multiple remote locations and delivers the gases to two or possibly more gas-monitoring instruments (e.g., mass spectrometers) has been developed. The system includes a transport (suction) pump that draws the gases from the sampling locations, through transport tubes, into a plenum, which is large enough to act as a buffer against changes in pressure in the transport tubes. Connected to each transport tube at a location near the plenum are two or more sample tubes that are, in turn, connected to manifolds of sample-selector valves through which gases are drawn into the instruments. Each instrument is equipped with a sampling (suction) pump that draws gas from one of the transport tubes that has been selected by opening the corresponding sample-selector valve. Each sampling pump is operated under feedback flow and pressure control to maintain a steady instrument-inlet pressure needed to ensure stable instrument readings. The sample flow thus diverted from the transport tube is kept to one-fifth or less of the transport flow in order to minimize the perturbation of the transport flow and thus, further, minimize any effect of one instrument on the other.

Posted in: Briefs, TSP, Physical Sciences, Gases, Test equipment and instrumentation, Spacecraft

Atmospheric Source of Atomic Oxygen for Cleaning Paintings

A vacuum chamber is no longer necessary.

A portable apparatus that operates at atmospheric pressure generates a beam of monatomic oxygen. The apparatus is designed to be used in a dry, noncontact process for removing organic contaminants from the surfaces of paintings. Organic contaminants that can be wholly or partly removed by use of this apparatus include some deposited in acts of defacement (e.g., lipstick and marks left by felt-tip and ball-point pens) and some deposited from fire (e.g., soot and charred binder). In some cases, this apparatus may make it possible to restore works of art that were previously counted as lost.

Posted in: Briefs, TSP, Physical Sciences, Maintenance, Repair and Service Operations, Maintenance, repair, and service operations, Oxygen

General-Purpose Wavelet Program

This program affords a variety of capabilities that are especially useful in wavelet analysis.

"S+Wavelets" is the name of a computer program that implements a suite of mathematical "tools" for wavelet analysis of signals (including two-dimensional signals that represent images.) Wavelets, being localized in both time and frequency (or space and wave number), serve as means for transforming and extracting information from signals that have temporally or spatially varying properties. In a sense, wavelet methods combine the best features of time and frequency methods (e.g., Fourier-transform methods). Modern wavelet research began in the mid-1980s, but until now, there has been no commercially available, general-purpose software to support rapid prototyping for research on, and application of, wavelets. S+Wavelets satisfies the need for such a computer code.

Posted in: Briefs, Information Sciences, Physical Sciences, Mathematical analysis, Rapid prototyping, Computer software / hardware, Computer software and hardware, Imaging, Imaging and visualization, Computer software / hardware, Computer software and hardware, Imaging, Imaging and visualization

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